This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. This project is a comparative study of normal and pathological brain aging in humans, chimpanzees, and other nonhuman primates, with the specific goal of understanding why humans are the only primates that develop Alzheimer's disease. We are using comparative neuroimaging to identify species differences and similarities in brain gray matter volume, white matter volume, and white matter integrity across age groups. In addition, we are comparing age-related changes in microscopic brain anatomy and molecular biology in postmorten tissue. This includes documenting the varieties of beta-amyloid oligomes in humans and nonhuman primates, including forms specific to humans, and identifying ligands that bind human-specific forms. In 2010, we completed and published a study of asymmetries in the corticospinal tract of chimpanzees compared to humans. In addition, we completed data analysis of comparative studies of aging in the optic nerves, corpus callosum, and major cerebral white matter tract, based on MRI data, and initiated a comparative study of white-matter hyperintensities. Also, we completed histological and MRI analysis of two chimpanzee stroke cases.